Detection and correction of reverse operation of a compressor in a refrigeration system

Abstract

A method and system for detecting and correcting unintended reverse or backward operation of an electric motor driven scroll compressor of a refrigeration system is characterized by monitoring the pressure at a suction side of the compressor during operation of the refrigeration and determining whether the pressure, after a first time interval following startup of the compressor, exceeds and remains in excess of a predetermined upper pressure limit for at least a second time interval. If it does, the compressor is turned off for a third time interval and is then restarted. The foregoing is repeated and if the compressor is turned off a selected number of times because of successive occurrences of high suction side pressures during operation of the refrigeration system in a chilling cycle, an error indication is generated and the refrigeration system is shut down.

1. A control system for a refrigeration system having an electric motor driven compressor, said control system comprising:
 means for sensing whether said compressor is on; 
 first means for determining whether compressor suction side pressure is at least equal to a predetermined pressure at the end of a first time interval following sensing that said compressor is on; 
 second means for determining whether compressor suction side pressure is at least equal to said predetermined pressure at the end of a second time interval following a determination at the end of said first time interval that compressor suction side pressure is at least equal to said predetermined pressure; 
 means for turning off said motor driven compressor for a third time interval in response to a determination at the end of said second time interval that compressor suction side pressure is at least equal to said predetermined pressure; and 
 means for turning on said motor driven compressor at the end of said third time interval. 
 
     
     
       2. A control system as in  claim 1 , wherein said electric motor driven compressor is an electric motor driven scroll compressor. 
     
     
       3. A control system as in  claim 1 , wherein said refrigeration system is operable in both chilling and defrost cycles, said sensing means further senses whether said compressor is on in a defrost cycle of said refrigeration system, and said first means for determining is responsive to said sensing means sensing that said compressor is on but not in a defrost cycle of said refrigeration system for determining whether compressor suction side pressure is at least equal to said predetermined pressure at the end of said first time interval. 
     
     
       4. A control system as in  claim 1 , further including:
 counter means for storing a count of the number of successive times that said compressor is turned off by said means for turning off said compressor; and 
 means responsive to the count in said counter means reaching a selected count for terminating operation of said refrigeration system. 
 
     
     
       5. A controller for a refrigeration system having an electric motor driven compressor, said refrigeration system comprising:
 means for monitoring refrigerant pressure at a suction side of said compressor; 
 means responsive to monitored suction pressure being at least equal to a predetermined pressure at selected times after said motor driven compressor is turned on for turning off said motor driven compressor; and 
 means for turning on said motor driven compressor a predetermined time after said means responsive turns off said compressor. 
 
     
     
       6. A controller as in  claim 5 , wherein said refrigeration system compressor is a scroll compressor. 
     
     
       7. A controller as in  claim 5 , including a frozen product dispenser, said refrigeration system having an evaporator heat exchange coupled to a freeze barrel of said frozen product dispenser and being operable to turn on said compressor in each of chilling and defrost cycles of said refrigeration system to chill and defrost said freeze barrel. 
     
     
       8. A controller as in  claim 7 , including:
 means for sensing when said compressor is on in a chilling cycle of said refrigeration system; 
 first timer means responsive to said sensing means sensing that said compressor is on in a chilling cycle of said refrigeration system for initiating timing of a first time interval; and 
 second timer means for initiating timing of a second time interval at the end of said first time interval if at the end of said first time interval monitored refrigerant pressure at said compressor suction side is at least equal to said predetermined pressure, said first and second time intervals being said selected times. 
 
     
     
       9. A controller as in  claim 8 , including:
 counter means for storing a count of the number of times said compressor is successively turned off by said means responsive and then turned on by said means for turning on; and 
 means responsive to a selected count in said counter means for terminating operation of said refrigeration system. 
 
     
     
       10. A refrigeration system having an electric motor driven scroll compressor operable in chilling and defrost cycles of said refrigeration system, said refrigeration system comprising:
 means for energizing said electric motor to turn on said compressor; 
 means for monitoring refrigerant pressure at a suction side of said compressor; 
 first timer means responsive to said compressor being turned on in a chilling cycle of said refrigeration system to initiate timing of a first time interval; 
 first means for comparing monitored compressor suction side pressure to a predetermined pressure and for generating a first signal if said monitored pressure is at least equal to said predetermined pressure at the end of said first time interval; 
 second timer means responsive to generation of said first signal to initiate timing of a second time interval; 
 second means for comparing monitored compressor suction side pressure to the predetermined pressure and for generating a second signal if said monitored pressure is at least equal to said predetermined pressure at the end of said second time interval; 
 means responsive to generation of said second signal for de-energizing said electric motor to turn off said compressor; 
 third timer means responsive to generation of said second signal for initiating timing of a third time interval; and 
 means for re-energizing said electric motor at the end of said third time interval to turn on said compressor in a chilling cycle of said refrigeration system. 
 
     
     
       11. A refrigeration system as in  claim 10 , including:
 counter means for counting the number of successive times that said electric motor is de-energized due to compressor suction side pressure being at least equal to said predetermined pressure at the end of said second time interval; and 
 means responsive to said counter means reaching a selected count to terminate operation of said refrigeration system. 
 
     
     
       12. A method of controlling a refrigeration system having an electric motor driven scroll compressor, said method comprising the steps of:
 energizing the electric motor to operate the compressor; 
 monitoring refrigerant pressure at a suction side of the compressor; 
 determining whether monitored refrigerant pressure is at least equal to a predetermined pressure both after expiration of a first time interval following energization of the motor and after expiration of a second time interval following expiration of the first time interval; 
 de-energizing the motor to turn off the compressor for a third time interval in response to said determining step determining that monitored compressor suction side pressure is at least equal to the predetermined pressure after expiration of each of the first and second time intervals; and 
 re-energizing the electric motor to operate the compressor following expiration of the third time interval. 
 
     
     
       13. A method of controlling a refrigeration system having an electric motor driven compressor, said method comprising the steps of:
 sensing whether the compressor is on; 
 determining whether compressor suction side pressure is at least equal to a predetermined pressure at the end of a first time interval following said sensing step sensing that the compressor is on; 
 ascertaining, in response to said determining step determining that compressor suction side pressure is at least equal to the predetermined pressure at the end of the first time interval, whether compressor suction side pressure is at least equal to the predetermined pressure at the end of a second time interval following the first time interval; 
 turning off the motor driven compressor for a third time interval in response to said ascertaining step ascertaining that compressor suction side pressure is at least equal to the predetermined pressure at the end of the second time interval; and 
 turning on the motor driven compressor at the end of the third time interval. 
 
     
     
       14. A method as in  claim 13 , wherein the electric motor driven compressor is a scroll compressor. 
     
     
       15. A method as in  claim 13 , wherein the refrigeration system is operable in chilling and defrost cycles, said sensing step senses whether the compressor is on in a defrost cycle of the refrigeration system, and said determining step is responsive to said sensing step sensing that the compressor is on but not in a defrost cycle of the refrigeration system to determine whether compressor suction side pressure is at least equal to the predetermined pressure at the end of the first time interval. 
     
     
       16. A method as in  claim 13 , including the steps of:
 counting the number of successive times of performance of said turning off step; and 
 terminating operation of the refrigeration system upon said counting step reaching a predetermined count. 
 
     
     
       17. A method of controlling a refrigeration system having an electric motor driven scroll compressor operable in chilling and defrost cycles of the refrigeration system, said method comprising the steps of:
 energizing the electric motor to turn on the compressor; 
 monitoring refrigerant pressure at a suction side of the compressor; 
 sensing whether the compressor is on in a defrost cycle of the refrigeration system; 
 initiating timing of a first time interval in response to said sensing step sensing that the compressor is on and not in a defrost cycle of the refrigeration system; 
 determining, after expiration of the first time interval, whether monitored pressure at the suction side of the compressor is at least equal to a predetermined pressure; 
 initiating timing of a second time interval in response to said determining step determining that monitored compressor suction side pressure is at least equal to the predetermined pressure after expiration of the first time interval; 
 ascertaining, after expiration of the second time interval, whether monitored compressor suction side pressure is at least equal to the predetermined pressure; 
 turning off the compressor in response to said ascertaining step ascertaining that monitored compressor suction side pressure is at least equal to the predetermined pressure after expiration of the second time interval; 
 initiating timing of a third time interval in response to performance of said turning off step; and 
 re-energizing the electric motor to turn on the compressor in a chilling cycle of the refrigeration system after expiration of the third time interval. 
 
     
     
       18. A method as in  claim 17 , including the steps of:
 counting the number of times of expiration of the third time interval; and 
 terminating operation of the refrigeration system upon said counting step reaching a selected count.